1. Field of the Invention
The present invention relates to a cleaning blade which is set in an image forming apparatus employing an electrostatic transfer process and which includes a blade member and a support member to rub and remove residual toner remaining on a photosensitive drum provided to the image forming apparatus.
The image forming apparatus employing an electrostatic transfer process, such as an electrophotographic copying machine, a laser beam printer and a facsimile, performs copying and printing by adhering toner to an electrostatic latent image formed on a photosensitive drum, and then transferring the toner image to copying paper. As a method of removing residual toner remaining on the photosensitive drum after transferring the toner image, a method has been put into practical use, which employs a cleaning blade having a blade member formed of urethane elastomer and a support member (holder).
2. Description of the Related Art
Conventionally, as a material forming such a blade member, a polyester urethane elastomer, particularly a thermosetting urethane elastomer, has been used which is excellent in mechanical strength such as abrasion resistance and is less likely to creep (permanent deformation due to contact stress).
The above-mentioned polyester urethane elastomer is usually produced by a prepolymer method, a semi one-shot method, a one-shot method, etc., using polyisocyanate, polyol, a chain extender, and a catalyst. In this production, a catalyst is added for shortening a molding cycle and improving production efficiency of the blade member. Conventionally, as such a catalyst, triethylenediamine (TEDA), dimethylimidazole (DMI), etc., have been used. However, the polyester urethane elastomer produced using the catalyst has such a problem that the above-mentioned catalyst remaining inside is vaporized by moisture in the air or heat, resulting in contamination of other parts. Then, as a result of other parts being contaminated by the above-mentioned catalyst, image defects may occur.
As a means for solving the problem, a case has been introduced in which a catalyst is used having 2 or 3 hydroxyl groups in a molecule (e.g., see Japanese Patent Application Laid-Open No. H07-290603). When a catalyst having such a feature is used, the hydroxyl groups contained in a molecule react with isocyanate contained in a prepolymer. Therefore, the catalyst can be prevented from exuding out of urethane elastomer. However, even when the catalyst has hydroxyl groups in a molecule, not all the hydroxyl groups react with isocyanate in a prepolymer. In such a case, an unreacted catalyst may be exuded out of urethane elastomer by moisture in the air or heat.
Since image forming apparatuses are miniaturized and are improved in image quality with the spread of an electrophotographic copying machine or a laser beam printer, a positional relationship with other parts becomes closer than before, or a space around a cleaning blade decreases. Therefore, even when the amount of the catalyst vaporized by moisture in the air or heat is small, other parts are liable to be contaminated, which results in a condition that image defects are likely to occur.